| As a world-famous water conservancy and hydropower project,the Three Gorges Project has played a very important role in flood control,navigation,power generation and other aspects since its completion.In order to further implement the state new development idea and development strategy,practice the new concept of flood resources utilization,in recent years,relevant departments and some scholars have proposed that “consider the new operating environment of the Three Gorges Reservoir and use the development results of new flood forecasting technology,Under the conditions of basically ensuring that the downstream flood control level does not decrease and the impact on the flood control of the reservoir area is acceptable,research and excavate the flood regulation capacity potential of the Three Gorges Reservoir,raise the operating water level of the Three Gorges Reservoir during the flood season,and fully develop and utilize the water resources of the Yangtze River,especially flood resources,” and the preliminary plan is to dynamically increase the water level of the Three Gorges in flood season from the original 145 m to 148 m,150m,152 m,and 155 m.In view of the new problems of reservoir bank stability caused by the adjustment of operating water level,it was selected some typical bank slopes improvement projects in the Wushan to Fengjie section of the reservoir area.Based on the limit equilibrium method and the unsaturated seepage theory,the transfer coefficient method was combined with the numerical simulation method,and the bank slope theoretical analysis model and the fluid-solid coupling numerical model are established to compare and study the slope stability changes under different operating water levels,and the impact of extreme conditions such as short-term water level drop and short-term rainstorm are also considered.The preliminary results as following:(1)According to the comparative calculation results of seven bank slope projects in Wushan(five actual projects)and Fengjie(two actual projects),it can be seen that after the operating water level increases,the stability coefficient of the bank slope has increased,it shows that the increase of 148 m and 150 m water levels is very small,and the increase in 152 m and 155 m is slightly larger.The increase is not large in general,which is beneficial to the stability of the bank slope.(2)In order to explore the changing laws of different permeability,seepage field and stability after operating water level adjustment,two typical slip-type bank slopes in Wushan～Fengjie section were selected,and the seepage-stress coupling model was used to calculate steady-transient seepage,stress and stability.The results of numerical simulation show that the stability of the bank slope still increases with the increase of the operating water level,and there is no obvious difference in the stability of the various water level schemes.(3)In view of the short-term rapid decline of the operating water level in the reservoir area during the flood season,two bank slopes were selected,and the stability coefficient changes at different reservoir water level dropping speeds were analyzed.The results showed that the rapid decline of the water level in the short term has an adverse effect on the bank slope stability.The faster the water level drops,the greater the intensity of the storm,the faster the slope stability declines,and the lower the minimum stability coefficient,and the high water level plan has a larger drop value than the low water level plan.(4)Comprehensive analysis,for the four proposed water level plans,it can be seen that raising the operating water level during the flood season shows a favorable trend for the bank slope stability of the Wushan-Fengjie section in the Three Gorges Reservoir area.In the water level operation scheduling during the flood season,attention should be paid to the impact of the short-term rapid decline of the water level on the stability of the bank slope.The higher the water level,the faster the decline,and the greater the impact. |
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